Receiving system for electromagnetic radiations.



L. DE FOREST, RECEIVING SYSTEM FOR ELECTROMAGNETIC RADIA TIONS.APPLICATIQN FILED MAY 5. 1910.

1,18%59& Patent d Apr. 6, 1915.

. principle of LEE DE FOREST, OF NEW YORK, N.

TELEPHONE &. TELEGRAPH RECEIVING SYSTEM FOR ELECTROMAGNETIC B-ADIATIONS.

To all whom it may concern: I t Be it'kno'wn that I, LEE DE Fonnsr, acitizen .of the United States, residing in'the city, county and State ofNew York, have made a certainnew and useful Invention ini forElectromagnetic Ita- Receiving Systems the following is a specidiations,of which fication.

This invention relates to'receiving sys terms for electro-magneticradiations."

The object of the invention is to provide a receiving system forelectromagnetic radlations 1n the transmission of 'WlIBlGSScommumcations WhlCl'l eliminates the troubles and annoyances arisingfrom interference or similar disturbances.

Other objects of-the invention will appear more fully hereinafter.

The invention consists substantially in the construction, combination,location and relations of elements, all as will be morefully hereinafterset forth, as shown in the accompanying drawings, and finally pointedout in the appended claims.

Loose coupling methods as commonly employed in wireless receivingsystems to prevent interference troubles,

varying the mutual inductance between the to such an'ext'ent that thereceiving circuit will not be acted upon by the oscillations set up inthe antenna circuit by the received radiations, unless the two'circuitsare veryit :is always found that very strong interfering oscillations orradiations can excite disturbing vibratory I oscillations in the tunedsecondary or recelving circuit of coueven ifthe natural frequency pledsystems, of said circuit is entirely different from that of theinterfering radiations unless the mu tual inductance of the antenna andreceiving circuits is made so small that the radi-.

-embodying the principles of my invention I wherein the circuit of thereceiving'device' or telephone,

sociated with ations which'it is desired to receive and detect are nolonger able to appreciably excite the tuned secondary or receivingcircuit,

It is amongthespecial objects and purposes of my present invention toprovide a receiving system which is not dependent oscillations due tothe same, and. completely Specification of Letters Patent.

of the legs of the its re'actance to a received 'wave trainvaries.

depend upon the antenna and receiving circuits In practice, howevercapacity arranged in one of the legs of the bridge system. Fig.

circuit.

the receiving antenna system, and I ass0ciate the receiver telephone anddetectorwith the saidbridging circuit. In carrying out I Patented-Apr.c, 1915. Application filed May 5, 1910. Serial No. 559,525.

Y., ASSIGNOE, -IBY MESNE ASSIGNMENTS, TO RADIO.

COMYANY. A CORPORATION OF DELAWARE.

my invention I so constructor arrange-one bridge arrangement thatgreatly with the frequency of the received wave train.

Many rangements of the bridge system may well serve the purposes of mypresent invention. One form Which 'I- have found efficient, reliable'andsatisfactory. for the purpose-is to arrange a capacity and an inductancein' shunt to each other in one of the legs of the bridge circuit.Another formfis to employ different constructions and aran inductancecoil in one of the legs of'the bridge circuit composed of a flat ribbonconductor with the coils thereof wound .in close relation to each otherso as' to give the greatest possible distribution of capacity.

Still another form is to construct the con-y 'denser in a similarmanner, that is with thin strips of flat'material with an interposedribbon dielectric, the flat strips being wound upon themselves toproduce as great aself inductance as possible.

ties of great inductance and capacity, and

My broad invention in-this respect, therefore, as defined in the claims,is not. to be limited or restricted to any specific means for securingthe characv ter-istics mentioned.

In the drawings Figure 1 is aview in diagram showing one arrangement ofbridge circuit arrangement for a receiving system and detector, isinductively asis a similar view showing inductance and shunt to eachother in 3 is a similar view showing the circuit of the receiver deviceor.teleplione, and the detector, conductively connected to the bridgeFig. 4 is a similar view showing .-In all these cases the object is tosecure the combined .quali thebridging circuit. -Fig. .2.

i the bridging conductor L C a compound bridge circuit arrangementembodying the principles of my invention,

Fig. 5 is a planview of the inductance I employ as one arrangement incarrying out my invention.

' Referring to Fig. 1, A designates the antenna and E, the earthconnection thereof, the bridge arrangement being interposed between theantenna and its earth connection. In one leg of the bridge circuit areconnected the variable capacity (J, and the adjustable inductance L andin the other leg thereof are connected the variable capacity C, and theadjustable inductance L In the bridging circuit is connected theinductance L and G The circuit R of the telephone IQCGlVR I T, anddetector D, is connected inductively to the bridging circuit. In thisarrangement in accordance with the principles of my invention theinductance or the capacity in one leg or the other of the bridgearrangement should be so constructed and arranged as to secure thecombined charac- .teristics of great inductance and capacity. One meansfor securing this is by employing a. specially constructed inductance asshown in Fig. 5, which consists of a fiat ribbon conductor M wound intheform of a coil, and completely insulated by interposed. insulation N.

Referring to the arrangement shown in Fig.1, if We designate by R, thereactance (to an alternating current of a given frequencyv n) of theupper left hand branch of the bridge circuit; by R that of the upperriglit .handbranch; by R that of the lower left hand branch; and by R,that of the lower right hand branch, then we know from the generaltheory of the \Vheatstone the bridge is balbridge that when 2 R4 anced,that is, no current will [low through But the re- 1 1 actance Rreactance R react- 1 ance R :L,w and reactance R :L w. Vhere n, as aboveindicated, is the frequency, or number of cycles per second of thealternating electro-motive force impressed on the antenna earth circuitA ,E, then 20:27am Substituting these values for R R R R, inthereactance equation above given, and dividing out common elements theexpression g is obtained which equation represents the necessarycondition for balancing such a bridge circuit-as is illustrated in Fig.1 as well as that illustrated in the other figures of the drawingprovided always that in each case the reactance in each of the two upperbranches of the bridge is a capacity reactance, and the reactance ineach of the lower branches is an inductive reactance. lVhere it isdesired simply to balance the bridge circuit against a given or definitefrequenc of received oscillations as for instance to preventinterference due to a iiearby power- .ful ti'ansin-i .tteii ',thearrangement shown in Fig. l is sutlicient. This is therefore thesimplest form of my invention. In this case a balance adjustment'foreach frequency wo uldbe'necessary were it not for the fact that inaccordance with my invention, as-

before explained, the inductances L L. are

so constructed that the reactances thereof vary with the frequency whichis the case where the inductance is constructed a very large conductorin which event'its reactance increases rapidly with the frequency, sothat while the bridgeis balanced for a given frequency and for allfrequenciesbelow the given frequency it becomes more and more unbalancedas the frequency increases above the given frequency.

Now with the branch circuit arrangement shown in Figs. 2, 3 and 4, thatis where inductances and capacities are arranged in shunt or seriesparallel to each other in one or another leg of the antenna earth bridgecircuit, such branch circuit, will have a capacity reactance, bysuitable relative adjustment, for all frequencies above a certain givenor critical frequency, and an inductive reactance for all frequenciesbelow that 'critical frequency. This given or critical frequency is thatwhich the circuit of C, L when in series is in tune, that is the naturalfrequency of vibration of this circuit when closed and considered alone.In other words when the period of the impressed electromotive force is I,P ZEN/141101 the reactance of this branch circuit becomes infinite.'\Vhen this condition obtains of course no current will flow through thatpart or leg of the antenna earth bridge circuit' which contains thebranch circuit and consequently the bridge conductor with which thetelephone receiver is associated becomes completely mbalanced. For thisClltlCillfrequency, therefore, the maximum difference of potential. willbe impressedacross the terminals of the bridge conductor, and if thenatural period of this conductor be tuned to this critical frequency,the maximum effects will be produced in the receiver circuit, associatedtherewith.

For'frequencies of received currents which lie above the criticalfrequency, as above defined, the reactance ofthe leg ofthe antennaearthbridge which contains the branch circuit is always a capacity reactance,and consequently by properly adjusting the capacity C, so that therelation holds v 2 1 the bridge conductor will be balanced and nocurrent will flow therethrough, and this strongly" marked above referredto,

conductor continues more or less in balance for all such frequencies,even if the capacity C, be not especially altered or adjusted to securea perfect balance. Similarly, as in ,the arrangement shown. in Fig. 4,for example, if the impressed frequency lies below the criticalfrequency, as above defined, of a. branch circuit L 0 the reactance ofthe leg containing this branch circuit becomes inductive, and, bysuitable'adjustment of L L 01 0 the mess g g may be not respond totraversing the bridging circuit due to radiate'd energy of some otherfrequency, does found, in practice, that by-thus adjusting the bridgeinductances and capacities to cut out interference from a givenfrequency of radiated wave trains, the same ad ustment 1s the givenfrequency. I have.

also sufliciently effective in eliminating ink terference due to allradiated waves of lower frequencies.

established and consequently the br idge conductor may thus be balanced,either perfectly or imperfectly for-any given frequency which lies belowthe critical frequency. If the impressed frequency, however, be abovethis critical frequency, the reactance of the branch L C becomes a ca--pacity reactance,

tionof its own, the reactance thereof becomes infinite for thatfrequency to which it is itself in tune, and it becomes a capacityreactance, for allfrequencies above and an inductive reactance for allfrequencies below that. frequency. A bridge circuit therefore, whichcontains such a distributed capacity coil in one of its legs can bebalanced for certain frequencies by a capacity in the conjugate leg,

le I

It will be notedthat insecurin'gthe best results certain preliminaryconditions should be observed Thus it' is-im'portant to tune thereceiver circuit R,'to the frequency of the wave trains to be received,and the entire antenna-earth bridge circuit should also be adjusted tillthe current generated therein from the radiations to be received is pfmax imum' intensity in said bridging circuit.

It is obvious that thereceiver circuit B, may be coupled up 'orassociated with the bridging circuit in many different ways. In

Figs. 1, 2 and 4, I have shown this circuit inductively associated withthe bridging cirsuit.

shown coupled up in series in the bridging circuit but in shunt with thecapacity C therein.

From the foregoing it will be seen that by or for certain other (lower)frequencies by an inductance in the conjugate After observing these andother usualconditions, when it is desired to cut-out the interferencedue to a given frequency of radiations then the inductances andcapacities in the legs of the bridge arrangement are ad-' justed until,with reference to the given free y.

thereby causing a balance in the bridging circuit, and hence thereceiver telephone, while responsive to currents they bear theproportional relation.

If desired the entire antenna-earth sys tern, in, may be tuned in theusual way, as for instance, b'y inserting a variable inductance LA, anda variable capacity C therein. In this manner closer preliminary tuningcan be effected in order to cut out a large partof the interferenceordinarily encountered, leaving the bridge arrangement of my inventionto eliminate any remaining interference. 1

In the arrangement illustrated in Fig. 4, as above indicated, I employone bridge arrangement with the inductance L and capacity C in one leg,and the combined inductance L and capacity pacity make thebridgingcircuit itself a bridge arrangeinentwith the inductance L, and c;-

C,, in one leg thereof, and the com' pacity bined inductance. L andcapacity C and the capacity C in the other leg, the receiver circuit Rbeing associated with bridgingcircuit of the secondary bridgearrangement;

In Fig. 3, the receiver circuit, R is C and'the ca-j 0,,1n series in theother leg, but ,I

including the bridgearrangement there- As indicatedin' the drawings therelation with respect to each otherof the inductance and capacity in anyleg of the bridgemay be changed without departure from the spirit andscope of my invention.

1 Similarly the capacity and inductance in the antenna-earth system maybe varied as to location, that is theseelements may be between theantenna and the bridge arrangement, or they may be between'the bridgearrangement and the earth.

Other variations and interchange of elements will readily suggestthemselves.

- What I-claim as new, and useful and of my own invention,and desire tosecure by Letters Patent is, 1. In a receiving system forelectro-magi'letic' radiations, an antenna system including branchesinparallel each containing inductance and capacity, a bridging circuitbetween said branches and a receiver circuit associated with saidbridging circuit.

i said branches, and a receiver circuit H580."

2. Ina receiving system for electromagnetic radiations, an antennasystem including branches in parallel, each containing inductance andcapacity elements, one of said elements combining the characteristics ofinductance and capacity, a bridging circuit. for

ciated with said bridging circuit.

3. In a receiving system forelectro-mag netic radiations, antenna systemincluding branches arranged in parallel one of said branches havingmeans to greatly vary its reactance to a received Wave train with thefrequency of such \vave train, a bridging cir cuit for said branches,and a receiver circuit associatedivith said bridgin circuit.

4. In a receiving system for electro-ma'gnetic radiations, an antennasystem, a circuit arrangement associated with the antenna system andincluding circuit elements in series parallel relation, a bridgeconnnecting like terminals of said circuit, a receivingcircuitconnections in series parallel relation, abridge connecting liketerminals of said series parallel connections, a receiving circuitassociated with the bridge, and means associated vvith thecircuitarrangement for balancing out oscillations produced by receivedradiations of a given frequency.

5. In a receiving system for electro-magnetic radiations-an antennasystem includ ing branches arranged in parallel, a bridging circuitintermediate said branches, secondary branches arranged in parallelinsaid bridging circuit, a secondarybridging c1r-' cuit intermediate saidsecondary branches, and a receiving circuit associated withsaidsecondary bridging circuit.

6. In a receiving system for electro-magnetic radiations, an antennasystem including interrelated branch circuits arranged in parallelrelation with respect to each other and having respectively branchingcircuits, a receiver circuit associated with one of said bridgingcircuits means for balancing out oscillations relating fromradiationshaving a frequency lower than that of the radiations to bereceived, and means for. balancing out oscillations relatingfromradiations having a fre uencv hi "her than that of the r. s. b V

radiations to be received. v

7. In a receiving system for electro-magnetic radiations, an antenna.system, 'a pre liminary bridge. circuit arrangement associate'dtherewith, a secondary bridge circuit arrangement associated with thebridging circuit of the preliminary bridge arrangement, and a receivercircuit associated with the bridging circuit of thesecondary bridgearrangementv 8. In a receiving system for electro-magnetic" radiations,an antenna system, a preliminary bridge circuit arrangement associatedWith the antenna system, a secondary bridge circuit arrangementassociated with the bridging circuit of the preliminary bridgearrangement, a receiver circuit asso: 'ciated with the bridging circuitof-the secondary bridge arrangement, means for adjusting the preliminarybridge arrangement to balance out oscillations resulting from receivedradiations having a frequency less than'tbat of the *adiations to bereceived and means for adjusting the secondary bridge arrangement tobalance out oscillations resulting from radiationshaving afrequencygreater than that of the radiations to be received.

9. In a receiving system for electro-rnagnetic radiiitions, an antennasystem, interrelated bridge circuit arrangements associated with theantenna system, a receiver circuit associated with the bridging circuitof one of said interrelated bridge arrangements, variable inductance andcapacitv elements arranged in the legs of the interrelated bridgearrangements, one of these elements in each of the bridge arrangementscombining the qualities of-inductance' and capacity. N

10. In a receiving system for electro-magnetic radiations, an antennasystem including branches in parallel one of said branches havinginductance andca-pacit-y arranged in shunt to each other, abridging'circuit between said branches and a receiver circuit ingabridge circuit arrangement, capacity' and inductance associated inshunt to each other in said bridge arrangement, a secondary bridgearrangement included in the bridging circuit of the first named bridgearrangement, capacity. and inductance in shunt to each other in thesecondary bridge arrangement, and a receiver circuit associated. withthe bridging circuit of the secondary bridge arrangement.

In testimony whereof I have hereunto set my hand in the presence of thesubscribing Witnesses, on this 18th'day of April A. 1).,-

- LEE nn FOREST.

Witnesses:

ll lan W- CLINTON, S. E. DARBY.

